Charge-air hoses serve to connect a turbocharger to a charge-air cooler (hot end) and to connect a charge-air cooler to the engine (cold end). Both ends have to withstand pressures up to 3 bar overpressure and also have to compensate for the relative movement between engine and charge-air cooler.
There are known charge-air hoses for charge-air lines and also cooling-water hoses for cooling-water lines which each have an extruded elastomeric inner layer onto which a tubular knit or a tubular braid has been knitted or braided. Extruded onto this there is an external layer made of elastomeric material. The extruded inner layer can be composed of one or more individual layers. Hoses of this type are flexible and pressure-resistant up to overpressures of about 3 bar.
In order to achieve higher pressure resistance, attempts have been made to arrange an intermediate elastomer layer and a further layer made of a circular knit or circular braid between the circular knit or circular braid and the extruded external layer. Although the higher pressure resistance was satisfactory, it was very difficult to produce complicated curved-hose geometries because the increased stiffness of this type of hose limits small radii of the hose curves and larger expansion at the ends of the hose.
There are also known wound hoses composed of one or more wound layers. The wound layers are composed of knit or woven material coated with an elastomeric material on one or both sides. These wound hoses are resistant to high pressure but create difficulties in further processing, since, as the number of wound layers increases, the increase in stiffness makes it difficult to produce hoses with expanded ends for the attachment of fittings, and hoses with complicated curved geometries.
United States patent application publication 2008/0000540 A1 discloses a flexible hose which has, embedded in an elastomeric wall, a pressure-resistant structure which comprises at least one pressure-resistant element that, in essence, takes the form of a filament or wire. The pressure-resistant structure is knitted onto the initially extruded elastomeric inner layer. An elastomeric external layer is then applied by extrusion. Although this is a flexible hose, it has low pressure resistance.
EP 1 013 979 A2 discloses a charge-air hose equipped with a pressure-resistant structure encompassing at least one woven material layer. The pressure-resistant structure is rubber-coated and is wound onto an auxiliary mandrel before it is introduced to the actual vulcanization process. By virtue of the plurality of wound layers, this wound hose is excessively stiff and difficult to mold to curved geometries.
Newly designed highly charged engines require hoses which comply with stringent requirements in relation to flexibility but are also suitable for high overpressures (greater than 3 bar). The automobile industry is constantly developing ever smaller engines with ever higher performance ratings per liter of cylinder volume and charge-air pressures are therefore ever higher with a resultant requirement for new hose systems for these pressures which give the same flexibility.
Hoses provided hitherto emphasize either flexibility or adequate pressure resistance, but not both simultaneously.